Research

Evaluation of the TRAF Family of Models Testing of the CORFLO and FRESIM Models

The final report describes the key findings of a Washington State Department of Transportation (WSDOT) and Federal Highway Administration (FHWA) project. The research was undertaken during the 1988-1989 time period using mainframe computer versions of the programs. Using Corridor Flow (CORFLO), the investigators modeled the traffic impacts on local and regional roadways that would be caused by the reconstruction of I-405 through the City of Renton, Washington, which is in the Seattle metropolitan area. Using Freeway Simulation (FRESIM), the investigators also modeled I-405 on the northeast side of Renton, where the high occupancy vehicle (HOV) lane, when completed, will transition from the inside to the outside of the freeway (across general purpose traffic).

Traffic volume data, traffic signal parameters, and roadway geometric data were obtained and used as needed in each of the computer traffic modeling programs.

The CORFLO model could not be adequately calibrated to represent existing traffic flow. The researchers could not determine whether the difficulties in calibrating the model were related to weaknesses in the model itself or to weaknesses in the input data. Use of the CORFLO mainframe computer program for construction traffic simulation by WSDOT is not recommended at this time. The program requires extensive, detailed data, which is usually unavailable and too costly to acquire given the resources normally available for this type of project. Modifying the CORFLO program to run on personal computers is suggested, and was released by McTrans in September 1992.

While the FRESIM model appeared to be able to handle the proposed HOV lane crossover, this could not be verified because the FRESIM output was so complex that it was unreadable. A graphic display of the FRESIM output as a supplement to the existing tabular output is recommended.